Components made of Shape Memory Alloys (SMA), such as TiNi, return to a predetermined form when heated from a relatively limp Martensitic state to a relatively stiff Austenitic state. This process is reversible. Some SMA components can even be trained to take on two distinct forms depending on their body temperature.
Bimetallic components can also perform in a similar way.
Applications abound in which electrical current is passed through to heat up such components to bring about the desired form change, which is exploited to perform some mechanical work. Such heating is due to the power dissipation of the electrical resistance inherent to the components and is by definition a classical ohmic phenomenon.
Even the basic expansion and contraction of material caused by heat and cold are sometimes exploited in this manner.
For example, U.S. Pat. Nos. 4,002,954 and 4,700,541 employ SMA components to perform triggering and positioning functions; bimetallic contacts that heat up . . . open . . . cool down . . . close . . . heat up . . . are extensively used in automobile turning lights, and U.S. Pat. No. 4,675,640 employs a bimetallic strip as a circuit breaker; U.S. Pat. No. 2,926,293 employs a simple metal wire as an actuator.
In all cases, including the aforementioned, electrical power is supplied by power supplies or batteries. This means that when power or batteries fail, these systems are rendered unusable. In cases such as electronic door locks or medical equipment, such disability can lead to catastrophe.
The use of batteries not only is costly, it also imposes a waste-disposal problem.
In many applications, such as in electronic door locks, electronic fishing reels, derailleur gears for bicycles, and cameras, system operation is always accompanied by an ample supply of mechanical energy. In accordance with U.S. Pat. No. 4,912,460, which is incorporated herein by reference, part of the mechanical energy is channeled to run an electric generator to provide the necessary electrical power for operating a decision making apparatus and for electrostatically moving a mechanical gate. Such a pseudo-mechanical system operates without external electrical power or batteries, thereby providing solutions to the cost, disability and waste disposal problems mentioned above. A problem with electrostatically moving the gate is that the plates of the electrostatic activator must be very close together whereby the amount of movement which results is relatively small leading to difficulties in design and very close tolerance requirements. The preferred apparatus of the U.S. Pat. No. 4,912,460 patent utilizes a piezoelectric bimorph in the nature of a conductor-ceramic-conductor-ceramic-conductor sandwich. On application of electrical charge the bimorph flexes only a very small amount, generally less than about 0.001 inch.
As evidenced by U.S. Pat. Nos. 4,864,824 and 5,061,914, microelectronic semiconductor processing technology is used to fabricate all kinds of ohmic electromechanical actuators, and it is common knowledge in the field of nanotechnology that minuscule electric motors can be fabricated with integrated circuit process technology and can be part of a semiconductor chip. The operation of these micro-actuators and micro-engines, because of their minute physical size, needs only submillijoule levels of energy which can be produced unobtrusively by miniature generators contained in, for example, embedded inside, systems incorporating such actuators and engines.
Modern electrical generators that convert mechanical energy into electrical energy have been around for over a hundred years. Electromagnetism, piezoelectricity, magnetostrictivity and other phenomena can all be utilized in implementing such generators. The technologies are well known to those versed in the art and are beyond the scope of the present invention.